Early findings of a new £1 million study launched last year have revealed that flying predators such as hoverflies, ladybirds and parasitic wasps are a vital component in the campaign to reduce pesticides on arable farmland.
This important new collaborative study, called 'Rebugging the system' is being undertaken by three leading research institutions including The Game Conservancy Trust, Rothamsted Research and Imperial College London. The project is funded by the RELU (Rural Economy and Land Use) programme, supported by Research Councils UK, Defra (Department for Environment, Food and Rural Affairs) and SEERAD (Scottish Executive Environment and Rural Affairs Department).
This summer, scientists from The Game Conservancy Trust carried out field trials to determine how effective predatory insects are at reducing aphid numbers - a process known as biocontrol.
In a controlled experiment, scientists released thousands of cereal aphids into specially designed enclosures located on arable farmland in Wiltshire. The rate at which ground and crop active predators controlled the aphid infestation was then compared by the scientists within the different types of enclosure.
The results of the experiment were revealing and showed that all natural predators are effective at eliminating aphids, but flying predators such as hoverflies and parasitic wasps are the best at reducing aphid numbers. Ground predators such as beetles and spiders are also beneficial but not as effective as their aerial counterparts. Where these friendly predators were completely excluded, the scientists measured a 100 fold increase in aphids in just a few weeks - demonstrating the speed at which aphids can take hold and infect a field of unprotected crops.
In addition to monitoring the impact of these beneficial predators on aphid populations, the scientists were also measuring the amount of good habitat needed to encourage these beneficial predators into the crops.
Dr John Holland, Head of Entomology with the Trust said, "To maximise the benefit of these friendly predators we need to work out how much good habitat such as conservation headlands, field margins and beetle banks is needed to attract these insects, and also what type of habitat. This first trial, which concentrated on grass and flower rich field margins, showed that to achieve the best pest control results farmers need to add pollen and nectar mixes which contain plants such as cow parsley, yarrow and hogweed to the grass margins. Simply by adding these plants to the margins can boost predator numbers considerably and thus increase their effectiveness.
Next season, the Trust's entomologists will investigate the proportion of the farm that needs to be devoted to insect-rich habitat, and they are currently looking for farmers who would like to participate in the next stage of this important RELU project. John Holland explains, "We are looking for farms that have 6m grass margins around their fields and are located within the southern counties of England. The findings of this study will be used to provide practical guidance to farmers on biological control through habitat manipulation."